The high performance and economical operation of internal combustion engines equipped with plunger type fuel injectors is dependent upon the precise adjustment of the injector stroke. Various proposals have been made for determining the initiation and the length of the injector stroke but each of these is attended by disadvantages and shortcomings avoided by this invention. One prior gauge utilizes a wiper arm rotatable about a stem insertable into a timing socket at the base of an injector plunger. The wiper is manually rotatable crosswise of the plunger end and engages the plunger surface lightly when the plunger is properly adjusted. If the gauge stem is not held strictly parallel to the plunger the resulting adjustment is erroneous. Furthermore, the accuracy of the adjustment is left to the varying judgement of different users as respects "light wiping pressure".
Other examples of prior art timing gauges are found in the U.S. Pats. to Boyd No. 4,098,233 and to Johnson No. 4,202,207. Boyd seeks to avoid the possibility of operating the first mentioned gauge at an angle to the plunger axis by a device having a countersunk collar loosely seating a headed stem. The collar is placed against the top of the plunger and with its stem seated in a timing bore at the base of the plunger. The injector plunger is then adjusted while the mechanic's finger is placed against the head of the stem. Adjustment ceases when the mechanic judges the stem head is flush with the adjacent end surface of the collar. Again the results achieved are dependent upon the mechanic's judgment, the sensitivity of his sense of touch, the calloused condition of his fingertips and their degree of cleanliness. Johnson seeks to avoid these shortcomings by utilizing a gauge having a reciprocated plunger supported within a sleeve insertable over a plunger and against a reference surface at its base. The gauge includes a light which remains inactive when the plunger is either too high or too low. The Johnson gauge is a complex assembly having numerous parts including an adjustable stop which must be precisely set and maintained in position. Moreover, and as is true of each of the other prior art gauges, his gauge must be held on the engine with one hand while the other is being used to adjust the rocker arm.